Level bubble illumination by means of a radioactive gas and a phosphor element



Feb. 13, 1968 J. D. AULT 3,368,287

LEVEL BUBBLE ILLUMINATION BY MEANS O GAS AND A I PHQR l .IME

Filed Ap 25, 4

RADIOACTIVE INVENTOR JOHN D. AULT ATTORNEYS United States Patent3,368,287 LEVEL BUBBLE ILLUMINATION BY MEANS OF A RADIOACTIVE GAS AND APHOSPHOR ELEMENT John D. Ault, Twickenham, Middlesex, England, assignorto Saunders Roe & Nuclear Enterprises Limited, Hayes, Middlesex,England- Filed Apr. 23, 1964, Ser. No. 362,144 Claims priority,application Great Britain, May 1, 1963, 17 ,088/ 63 Claims. (Cl. 33-211)This invention relates to illumination of the bubble of a level or likeinstrument by light sources of the selfluminous type for use, althoughnot exclusively, with surveying equipment.

It is current practice to illuminate equipment of this type withluminous paint, but this suffers from some serious disadvantages. Thedegree of light intensity of luminous paint currently reaches itspractical limit at approximately 50 micro lamberts and this intensity isinadequate to permit close positioning of the bubble of a level, andalso requires a period of time for darkness adaptation. There aredifficulties associated with increasing this light intensity, as theRadioactive Substances Act 1960(a) limits the quantity of isotope insolid form to an amount that does not permit suflicient luminous paintto be used to produce a satisfactory light level.

Even at a light level of 50 micro lamberts the light life of luminouspaint is probably no more than one year, and replacement of such paintis both expensive and hazardous.

It is, therefore, an object of the invention to provide a levellingbubble with means of illumination which is self-luminous and comparedwith current means has a relatively high degree of brightness, a longlight life and generates negligible radiation external to itself.

The invention consists in means for illuminating the bubble of a levelor like instrument by self-luminous light source means of the typecomprising a phosphor excited to luminescence by a gaseousradionucleide.

Such means of illumination provides a greatly improved lig-ht level inthe region of from 200 to 400 micro lamberts without significantexternal radiation, and a useful light life of approximately twentyyears. The radioactive source uses less than two curies of tritium gas,and at this level persons using the device are exempted fromregistration under the Radioactive Substances Act 1960(a).

These and further objects and advantages of the invention will becomemore readily apparent from the following detailed description of variousembodiments of the invention which are by way of example only withreference to the accompanying drawings, wherein:

FIGURE 1 is a longitudinal section of a means of illuminating the bubbleof a level according to the invention.

FIGURE 2 is a transverse section along IIII of FIG- URE 1.

FIGURE 3 is a transverse section of a second embodiment of the inventionindicating an alternative way of attaching the means of illumination tothe chamber containing the bubble.

FIGURE 4 is a longitudinal section of a still further embodiment of theinvention wherein the self-luminous light source is enclosed within thechamber containing the bubble.

Referring to FIGURES l and 2, a level chamber 1, such as in commoncurrent use containing spirit 2, a bubble 3, and registering marks 4 isoptically sealed to a luminescent source 5 'at a surface 6 which isground flat in a transverse direction.

3,358,287 Patented Feb. 13, 1968 The luminescent source 5 consists of aglass tubular envelope which is internally coated with a phosphor 7having luminescent properties. Sealed within the said glass envelope isa radionucleide gas 8, preferably tritium, which bombards the phosphor 7with beta radiation particles to excite it into luminescence. The outersurface of the luminescent source 5 is coated on all sides, other thanthat which is optically sealed to the bubble chamber, with suitablereflective means 9. The bubble chamber 1 and the luminescent source 5are mounted for protection within a shockproof mounting 10.

FIGURE 3 shows a alternative method of positioning the luminescentsource 5 with respect to the bubble chamber 1 using a bond of opticallyclear rubber such as Silcoloid, a registered trademark. This methodobviates the necessity of forming flat ground faces on the bubblechamber 1 or on the luminescent source 5.

FIGURE 4 shows a further embodiment of the invention wherein theluminescent source 5 is secured within the bubble chamber 1 to provide amore compact unit.

In operation of the invention, when viewed from the direction facing theregistering marks 4, the luminescent source 5 provides a backgroundillumination of the bubble 3, enabling the bubble to be clearly observedwhen adjusting the bubble chamber 1 or any associated housing toposition the bubble 3 between the registering marks 4. Furthermore, theliquid 2 in the bubble chamber 1 tends to produce a dark outline aroundthe bubble 3 when viewed against the bright background.

To those skilled in the art it will be obvious that numerousmodifications 'and refinements may be made without departing from thescope of the invention. For example, more than one luminescent sourcemay be provided around the bubble chamber or within it. The shape of theluminescent source may be varied in any way in order to illuminate thebubble more conveniently. For example, with bubble chambers of theoblate spheroid type, where the bubble is positioned towards the centreof a circular surface of the oblate spheroid for levelling in more thanone direction, the luminescent source may also take the form of anoblate spheroid or other convenient circular horizontal cross-sectionfor more satisfactory illumination.

Furthermore, instead of the luminescent source being coated withreflective means the shockproof housing may provide reflective means,for example by being coated with reflective material or by beingmanufactured of white rubber or other suitable reflective material. Thebubble chamber, the luminescent source or the shockproof mounting may beprovided for some applications with attachment means. For extraprotection the whole device may be protected with an abrasive resistantsheath of transparent material or any other material provided withappropriately situated windows.

In a situation where the device is in no danger of fracture theshockproof mounting may even be omitted.

I claim as my invention:

1. A level indicating device comprising: an outer casing having a windowopening, an elongated first chamber mounted in the casing and filledwith a liquid except for a movable gas bubble located therein, a firstside of said first chamber being visible through the said casing windowfor observing the position of the bubble, a second elongated chambermounted in the said casing so that its center lies on the side of thecenter of the first chamber away from the said window, said secondchamber comprising a self-luminous light source including a phosphorousmaterial on the internal surface of the second chamber, and aradioactive tritium gas within said second chamber for exciting the saidphosphor material to luminescence, and a reflective surface located onthe side of the second chamber away from the first side.

2. A level indicating device as claimed in claim 1 wherein the saidsecond chamber is positioned Within the said casing adjacent the firstchamber on the side thereof away from the said Window, the facingsurfaces of the first and second chambers being ground fiat andoptically sealed to each other 3. A level indicating device as claimedin claim 1 wherein the said second chamber is spaced from the firstchamber within said casing by an optically clear rubber.

4. A level indicating device as claimed in claim 1 wherein the saidsecond chamber is located Within the first chamber adjacent the side ofthe first chamber away from the said Window.

5. A level indicating device as claimed in claim 1 wherein the saidouter casing is of a shockproof material.

References Cited 3,038,271 6/1962 MacHutchin et al. 250-106 X ARCHIE R.BORCHELT, Primary Examiner.

1. A LEVEL INDICATING DEVICE COMPRISING: AN OUTER CASING HAVING A WINDOWOPENING, AN ELONGATED FIRST CHAMBER MOUNTED IN THE CASING AND FILLEDWITH A LIQUID EXCEPT FOR A MOVABLE GAS BUBBLE LOCATED THEREIN, A FIRSTSIDE OF SAID FIRST CHAMBER BEING VISIBLE THROUGH THE SAID CASING WINDOWFOR OBSERVING THE POSITION OF THE BUBBLE, A SECOND ELONGATED CHAMBERMOUNTED IN THE SAID CASING SO THAT ITS CENTER LIES ON THE SIDE OF THECENTER OF THE FIRST CHAMBER AWAY FROM THE SAID WINDOW, SAID SECONDCHAMBER COMPRISING A SELF-LUMINOUS LIGHT SOURCE INCLUDING A PHOSPHOROUSMATERIAL ON THE INTERNAL SURFACE OF THE SECOND CHAMBER, AND ARADIOACTIVE TRITUM GAS WITHIN SAID SECOND CHAMBER FOR EXCITING THE SAIDPHOSPHOR MATERIAL TO LUMINESCENCE, AND A REFLECTIVE SURFACE LOCATED ONTHE SIDE OF THE SECOND CHAMBER AWAY FROM THE FIRST SIDE.